Jeep Grand Wagoneer 1990 - H - TESTS W/O CODES 1990 ENGINE PERFORMANCE Trouble Shooting - No Codes

Jeep Grand Wagoneer 1990 - INTRODUCTION

Before attempting to diagnose symptoms or intermittent faults, ensure steps in BASIC TESTING and TESTS W/CODES (if applicable) articles have been performed. Use this article to diagnose driveability problems that exist when a hard fault code is not present or vehicle is not equipped with a self-diagnostic system.

Symptom checks are intended to direct the technician to malfunctioning component(s) so that further diagnosis may be performed. A symptom should lead to further testing of specific components or systems, or verification of adjustment specifications.

Use intermittent test procedures to locate intermittent driveability problems that do not occur when the vehicle is being tested. These problems may cause a noticeable driveability problem or cause the MALFUNCTION warning light to illuminate on some vehicles.

It is also possible that certain driveability concerns have been rectified by the manufacturer through substitution of a revised calibration chip or computer control unit. Check with manufacturer for latest information on updated chips and control units.

NOTE:

For specific testing procedures, refer to SYSTEM/COMP TESTS article. For verifying specifications, refer to ADJUSTMENTS or SPECIFICATIONS article.

Jeep Grand Wagoneer 1990 - SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless the problem is actually happening while the vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC TESTING and TESTS W/CODES (if applicable) articles have been performed before attempting to diagnose a symptom. Symptoms available for diagnosis include the following:

• Rough Idle
• Poor Fuel Mileage
• Erratic Timing Advance
• Timing Not Affected By Vacuum
• Engine Fails To Start
• Engine Backfires, Fails To Start
• Engine Continues To Run With Key Off
• Engine Starts, Then Dies
• Hard Starting
• Poor High Speed Operation
• Ping Or Knock On Acceleration

Jeep Grand Wagoneer 1990 - ROUGH IDLE

Check spark plugs, spark advance, ignition system wires and connections, starter solenoid for internal shorting (except 2.5L), and trigger wheel pin. See BASIC TESTING article. See SYSTEM/COMP TESTS article regarding the following procedures.

• Check MAP sensor circuit and vacuum hose.
• Check injector harness connectors.
• Check coolant temperature sensor for shorted sensor or circuit.
• Check for proper idle control system operation.
• Check for shorted, open or misadjusted TPS.
• Check EGR valve operation.
• Check for shorts or opens in oxygen sensor circuit.
• Check PCV valve operation.

Jeep Grand Wagoneer 1990 - POOR FUEL MILEAGE

Verify ignition timing and spark advance are correct. See BASIC TESTING article. Check ECU for proper operation. See SYSTEM/COMP TESTS article.

Jeep Grand Wagoneer 1990 - ERRATIC TIMING ADVANCE

Check vacuum advance mechanism and centrifugal advance weights. See SYSTEM/COMP TESTS article.

Jeep Grand Wagoneer 1990 - TIMING NOT AFFECTED BY VACUUM

Check vacuum advance mechanism and adjusting screws. See SYSTEM/COMP TESTS article. Check pickup coil pivot for corrosion. See BASIC TESTING article.

Jeep Grand Wagoneer 1990 - ENGINE FAILS TO START NO SPARK AT PLUGS

Check for open, loose, or corroded ground wires in distributor, and check primary wiring circuits. See BASIC TESTING article. Check for defective ignition module, cracked distributor cap, defective rotor. See BASIC TESTING article.

Jeep Grand Wagoneer 1990 - CRANKS NORMALLY WITH SPARK AT PLUGS

Check vacuum and wiring connections. See SYSTEM/COMP TESTS article. Check fuel for water or alcohol and check fuel tank residual pressure valve. See SYSTEM/COMP TESTS article. Verify proper operation of fuel pump, relay and wiring. See BASIC TESTING article. Check for an open in coolant temperature sensor circuit. See SYSTEM/COMP TESTS article. If engine is warm, check for flooding. See BASIC TESTING article. On 4.0L with automatic transmission, check if crank position sensor and grommet have been updated. New sensor and grommet are available from manufacturer. If replacement of sensor and grommet fail to correct condition, check ECU. See SYSTEM/COMP TESTS article.

Jeep Grand Wagoneer 1990 - ENGINE BACKFIRES, FAILS TO START

Verify ignition timing is correct, check for moisture in distributor or faulty distributor cap and verify that ignition wires are connected in proper firing order. See BASIC TESTING article.

Jeep Grand Wagoneer 1990 - ENGINE CONTINUES TO RUN WITH KEY OFF

Check for defective starter motor solenoid. See SYSTEM/COMP TESTS article. Check for shorted diode in alternator warning light circuit. See SYSTEM/COMP TESTS article.

Jeep Grand Wagoneer 1990 - ENGINE STARTS, THEN DIES

Check choke vacuum kick setting and low carburetor fuel level on carbureted engines. See BASIC TESTING article. Check fast idle RPM speed, cam index and fuel pressure. See BASIC TESTING article. Inspect vacuum system for leaks. See SYSTEM/COMP TESTS article. On 4.0L with automatic transmission, check if crank position sensor and grommet have been updated. New sensor and grommet are available from manufacturer. If replacement of sensor and grommet fail to correct condition, check ECU. See SYSTEM/COMP TESTS article.

Jeep Grand Wagoneer 1990 - HARD STARTING

Check idle control, EGR valve and control circuits for proper operation. See SYSTEM/COMP TESTS article. Check for A/C ON signal at ECU and for overcharged A/C system. See SYSTEM/COMP TESTS article. Verify injector circuits and fuses for proper operation and check for restricted fuel lines. See BASIC TESTING article.

Jeep Grand Wagoneer 1990 - POOR HIGH SPEED OPERATION

Check fuel pump and lines for proper pressure. See BASIC TESTING article. Check ignition system wires for cracks or poor connections. See BASIC TESTING article. Check for restricted air cleaner or exhaust system. See BASIC TESTING article. Check MAP sensor and oxygen sensor circuits for opens or shorts. See SYSTEM/COMP TESTS article. Check ECU ground connection for resistance and check VSS signal against speedometer. See SYSTEM/COMP TESTS article.

Jeep Grand Wagoneer 1990 - PING OR KNOCK ON ACCELERATION

Check for shorts or opens in knock sensor and barometric sensor circuits. See SYSTEM/COMP TESTS article. Check ignition timing. See BASIC TESTING article. Check coolant system, belts and fan for proper operation. See SYSTEM/COMP TESTS article.

Jeep Grand Wagoneer 1990 - INTERMITTENT PROBLEM DIAGNOSIS

Intermittent fault testing requires the duplication of circuit or component failure, in order to identify the fault. These procedures may lead to the computer recording a fault code (on some systems) which may help in diagnosis.

If problem vehicle does not produce fault codes, it will be necessary to monitor voltage or resistance values using a DVOM while attempting to reproduce conditions which will create an intermittent fault. A change in status on the DVOM will indicate a fault has been located.

When using a voltmeter to pinpoint faults, monitor voltage reading with ignition on, or vehicle running. A change in status on the voltmeter while performing intermittent test procedures will indicate area of fault.

When using an ohmmeter to detect problems in the circuit, monitor circuit resistance (ohms) with ignition switch in the OFF position, or with battery disconnected. A change in ohmmeter reading while performing test procedures will indicate area of fault.

Jeep Grand Wagoneer 1990 - TEST PROCEDURES INTERMITTENT SIMULATION

To reproduce the conditions which create an intermittent fault so that it may be identified during testing, some of the following methods may be used:

• Applying light vibration to components.
• Heating a component.
• Wiggling or bending a wiring harness.
• Applying humidity to a component.
• Remove or apply a vacuum supply source.

Monitor circuit/component voltage or resistance while attempting to simulate intermittent. If vehicle is running, monitor for self-diagnostic codes. Use the results of these tests to identify a faulty component or an area which should be checked closely for the problem.